When a VARBINARY(MAX) column is marked with the FILESTREAM attribute, the limitation of 2GB is not applicable on the value any more. You can store values larger than 2GB in such a column. The maximum size is limited only by the size of the disk.
A FILESTREAM column can be accessed from TSQL, just like you access any VARBINARY(MAX) column. To find the size (number of bytes occupied) of a FILESTREAM column, you can use the DATALENGTH() function.
SELECT DATALENGTH(ColumnName) AS SizeOfDataFROM TableName